Conventionally and currently general manufacturing method uses lead by adding it to zinc the main active material for battery anode for corrosion resistance against electrolyte. Especially in batteries with neutral to acid electrolyte such as manganese dry batteries 0.15 to 0.50 percent by mass (%) of lead is added to anode zinc.
Further, addition of lead is for process ability of a zinc sheet. Anode zinc cans of cylindrical manganese dry batteries are generally made by extrusion molding of a zinc sheet of anode material in a heat from 100 degrees Centigrade to 260 degrees Centigrade, and an anode zinc plate for the laminated dry battery 6F-22 is made by punching a thinly rolled zinc sheet into a designed shape. But a pure zinc sheet is hardly extruded or punched to produce usable cans or plates. Therefore lead is added to help also process ability. But lead is one of environmental hazardous materials, so supply of anode zinc material without lead is now urgently needed and development of such materials is conducted enthusiastically.
Impact extrusion or deep drawing of a rolled zinc sheet is a way to make an anode can with a bottom cover. Such processes are possible cause of electrolyte leakage when a battery is excessively discharged and a zinc can partly wears extraordinarily. How to solve this problem of electrolyte leakage is a crucial issue for quality improvement of manganese dry batteries. Another environmental crucial issue is scrapping batteries (lead therein) in or together with home wastes.
Realization of lead additive-free active material for a zinc battery anode is a paramount necessity of today.
Technical development has been conducted for a long time to create active material for a zinc battery anode without adding lead and yet ensuring corrosion resistance and enough process ability. But so far none is successful to fulfill both requirements, and a battery lead additive-free is not available. Shortcomings of the technical development are in corrosion resistance and in process ability.
For example, corrosion test; the method is to dip a sheet of an anode zinc sheet into battery electrolyte and measure decrease of the sheet weight on picking out of electrolyte for evaluation of material corrosion resistance. It is an adequate method for material evaluation, but wearing process of the anode zinc material by discharge reaction of a battery is not taken into account which is essential factor to consider practical use of a battery. And consideration lacks as to impurities by elution from cathodes material, a compound of manganese dioxide, electrolyte and conductive material. As for process ability development works did many about material hardness, deformation and dent after extrusion or deep drawing but the works have been unable to find a material fault causing microscopic defects.
There is a development case presenting use of an alloy of zinc adding some or at least any one of indium, aluminum, and gallium instead of lead for a battery anode can. (Reference: JP6-196156A) This technology was developed focusing on crystal grain diameter and corrosion resistance of anode zinc material.
The technology enables to produce a same level of material as lead added zinc material by maximum addition of indium, in corrosion resistance as 0.82 mg/cm2. The test electrolyte contains inevitable impurities such as Ni, Co, and Cu. And, the technology lacks anticipation of impurities which elute from the cathode compound material when a battery is stored for a long period or at the time of discharge halt in an intermittent discharging. Because of aforesaid flaw, it is difficult to deem the anode material by this technology useable enough for practically marketable batteries.
Another known technology is a method to prevent corrosion of anode by adding bismuth to active material for zinc anode while limiting amount of nickel, cobalt, and copper to add to manganese dioxide, the active material for cathode. (Reference: JP7-45272A) A problem with this technology is inability of controlling cracks among material crystals entailed during process of anode zinc cans, being little study seems to have been made about microscopic structure of anode materials. So this method is not competent enough to ensure reliability of battery quality for a long time. By this method corrosion due to impurities eluted from the cathode compound material is deemed not to be sufficiently deterred from growing, so battery quality can not be stable. In applying this method, anticorrosion material was necessary to add to the anode zinc can material, for no consideration is given in the method as to reactive wearing process of a can to be caused by discharge reaction of a battery.